Résumé :
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Experiments were conducted to probe the interactions between natural dissolved organic matter (DOM) and two xenobiotics, and to determine how DOM influences their bioavailability. The experimental set-up, using dialysis bags, was designed to expose test organisms to the same constant concentration of free dissolved chemical, while increasing the concentration of the bound-to-DOM fraction. Daphnia magna S. Were exposed to pyrene or 2,2',5,5'-tetrachlorobiphenyl in the presence of 0, 1, 2, 5, 10 or 20 mg L-1 of a reference riverine humic acid (Suwannee River Humic Acid). The physico-chemical parameters were well constrained in the microcosm, demonstrating its potential usefulness. However bioaccumulation by D. Magna showed important variability between replicate treatments, sufficient to mask any trends as a function of DOM concentration. The organic-carbon-normalised partition coefficients (K-OC) ranged from 52000 to 92000 L kg(-1) for pyrene and from 8200 to 89000 L kg(-1) for 2,2',5,5'-tetrachlorobiphenyl, with a marked 'concentration effect' for the latter compound. (C) 1998 Elsevier Science Ltd. All rights reserved.
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